This invention relates generally to the chemical modification of substrate surfaces so as to provide a pattern thereon, and more particularly relates to the formation of a patterned surface using a microcontact printing technique followed by surface-initiated synthesis of polymer brushes within the framework of the pattern.
The generation of complex patterns in polymer films is traditionally achieved by combining spin-casting and photolithographic techniques. Polymer films patterned by this procedure are widely used for the fabrication of microelectronic devices or as selective barriers to etchants and redox-active probes. While successful, the utility of these patterned polymer films is restricted by their limited stability to solvents and subsequent chemical reaction, and difficulties in their preparation over large areas and complicated topographies. To address these latter challenges, whitesides and coworkers have introduced the concept of microcontact printing (xcexcCP) for the preparation of patterned self-assembled monolayers (or xe2x80x9cSAMsxe2x80x9d) on both planar and curved surfaces; see, e.g., Jackman et al. (1995) Science 269:994. This xe2x80x9csoft lithographyxe2x80x9d technique involves transfer of a molecular moiety from an elastomeric stamp to a substrate surface. The molecular moiety is such that self-assembled monolayers spontaneously form upon transfer from the stamp to a substrate. As is known in the art, self-assembled monolayers result from the chemisorption and self-organization of functionalized, long-chain organic molecules.
Self-assembled monolayers formed from alkanethiols on gold and silver have been studied extensively and proposed for use as barriers to wet chemical etchants (Kumar et al. (1994) Langmuir 10: 1498; xia et al. (1998) Angew. Chem. Int. Ed 37:550). In this approach, however, the utility of self-assembled monolayers as barriers to etchants is compromised by the susceptibility of monolayer films to formation of defects (Kumar et al. (1992) J. Am. Chem. Soc. 114:9188), their lack of barrier properties when using dry etchants such as reactive ions, and the conflicting time scales necessary for complete formation of SAMs and for high resolution patterning (Delamarche et al. (1998) J. Phys. Chem. B. 102:3324).
This invention is addressed to the above-mentioned limitations in the art, and provides a new method of using soft lithography to manufacture patterned surfaces, wherein polymerization is employed as a tool to chemically amplify surfaces already patterned with SAMs and thus provide a macromolecular barrier to etchants and the like. The preparation of a macromolecular barrier instead of a molecular one provides a means to mask defects within self-assembled monolayers and introduce resistance to a wide range of etchants. In addition, high resolution patterning is achieved by using surface-initiated polymerization to mask incomplete regions of SAMs and minimize lateral transport of the molecular moieties contained therein.
Accordingly, it is a primary object of the invention to address the above-mentioned need in the art by providing a method for preparing a substrate having a patterned surface, wherein the pattern is comprised of a self-assembled monolayer of molecular segments having an overlying polymer xe2x80x9cbrushxe2x80x9d layer covalently bound thereto.
It is another object of the invention to provide such a method which involves formation of a first self-assembled monolayer within predetermined regions of a substrate surface and subsequent deposition of a second self-assembled monolayer on the remainder of the substrate surface, followed by surface-initiated polymerization to provide a brush polymer pattern using functional groups present within the second self-assembled monolayer as polymerization initiation sites.
It is still another object of the invention to provide such a method wherein the first self-assembled monolayer is comprised of an inert molecular segment that is transferred to the substrate surface from a patterned stamp using a microcontact printing technique.
It is yet another object of the invention to provide a method for preparing a substrate having a patterned surface comprised of a self-assembled monolayer of molecular segments having an overlying polymer xe2x80x9cbrushxe2x80x9d layer covalently bound thereto, wherein the method involves formation of a first self-assembled monolayer within predetermined regions of a substrate surface and optional deposition of a second self-assembled monolayer on the remainder of the substrate surface, followed by surface-initiated polymerization to provide a brush polymer pattern using functional groups present within the first self-assembled monolayer as polymerization initiation sites.
It is a further object of the invention to provide a method for etching a conductive substrate surface by preparing a self-assembled monolayer on the substrate surface in the form of a pattern, leaving the remainder of the substrate surface exposed, conducting surface-initiated polymerization to provide a brush polymer pattern using functional groups present within the self-assembled monolayer as polymerization initiation sites, and etching the exposed surface with a chemical etchant.
It is still a further object of the invention to provide such a method which further comprises removing the organic material from the substrate surface after etching.
Yet another object of the invention is to provide surface-modified substrates having a patterned surface comprised of a self-assembled monolayer of molecular segments having an overlying polymer brush layer covalently bound thereto.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In a first embodiment of the invention, then, a method is provided for preparing a substrate having a patterned surface, comprising:
(a) providing a substrate having a surface to which molecular moieties can covalently bind;
(b) identifying predetermined regions on the substrate surface that correspond to a desired surface pattern;
(c) derivatizing the substrate surface by contacting the predetermined regions of the surface with a molecular moiety A-B, wherein A is a reactive terminus and B is an inert segment, under conditions effective to bring about covalent binding of the molecular moiety A-B to the surface through the reactive terminus A, thus providing surface-bound B segments in the predetermined regions with the remainder of the surface comprised of unmodified regions;
(d) contacting the derivatized substrate surface provided in step (c) with a molecular moiety Axe2x80x2-L-C, wherein Axe2x80x2 is a reactive terminus and may or may not be the same as A, L is a linker, and C is a molecular segment terminating in a functional group, under conditions effective to bring about covalent binding of the molecular moiety Axe2x80x2-L-C to the unmodified regions of the substrate surface through the reactive terminus Axe2x80x2, whereby a modified substrate surface is provided having surface-bound B segments in the predetermined regions and surface-bound C segments on the remainder of the surface; and
(e) contacting the modified surface provided in step (d) with a polymerizable composition under conditions effective to result in the synthesis or covalent attachment of a polymer to the functional groups of the surface-bound C segments.
In an alternative embodiment of the invention, a method is provided for preparing a substrate having a patterned surface, comprising:
(a) providing a substrate having a surface to which molecular moieties can covalently bind;
(b) identifying predetermined regions on the substrate surface that correspond to a desired surface pattern;
(c) derivatizing the substrate surface by contacting the predetermined regions of the surface with a molecular moiety Axe2x80x2-L-C, wherein Axe2x80x2 is a reactive terminus, L is a linker, and C is a molecular segment terminating in a functional group, under conditions effective to bring about covalent binding of the molecular moiety Axe2x80x2-L-C to the surface through the reactive terminus Axe2x80x2, thus providing surface-bound -L-C segments in the predetermined regions, with the remainder of the surface comprised of underivatized regions;
(d) optionally modifying the underivatized regions by contacting those regions with a molecular moiety A-B, wherein A is a reactive terminus and may or may not be the same as Axe2x80x2 and B is an inert segment, under conditions effective to bring about covalent binding of the molecular moiety A-B to the surface through the reactive terminus A, thus providing surface-bound B segments in the underivatized regions; and
(e) contacting the provided in step (c) or step (d) with a polymerizable composition under conditions effective to result in the synthesis or covalent attachment of a polymer to the functional groups of the surface-bound C segments.
In another embodiment of the invention, a method is provided for etching an electrically conductive substrate surface, comprising:
(a) providing a substrate having an electrically conductive surface;
(b) identifying predetermined regions on the electrically conductive surface to be protected from etching;
(c) contacting the predetermined regions with a molecular moiety Axe2x80x2-L-C, wherein Axe2x80x2 is a reactive terminus, L is a linker, and C is a molecular segment terminating in a functional group, under conditions effective to bring about covalent binding of the molecular moiety Axe2x80x2-L-C to the surface through the reactive terminus Axe2x80x2, thus providing surface-bound -L-C segments in the predetermined regions with the remainder of the surface comprised of unmodified, exposed regions; and
(d) contacting the surface derivatized in step (c) with a polymerizable composition under conditions effective to result in the synthesis or covalent attachment of a polymer to the functional groups of the surface-bound C segments; and
(e) contacting the surface modified in step (d) with a reagent that is selected to degrade the unmodified, exposed regions of the electrically conductive surface but that is inert with respect to the surface-bound polymer.
Preferably, following step (e), the method further includes removing the surface-bound -L-C groups and the polymer to uncover the predetermined regions of the electrically conductive surface.
In a further embodiment of the invention, substrates having modified, patterned surfaces are provided that can be prepared using the methods described and claimed herein. The patterned substrates may be microelectronic devices, or they be biosensors, high-density bioassay plates, or the like. The preferred use of the invention is in the fabrication of microcircuitry such as microelectronic resistors, transistors, capacitors and circuit breakers.